   inf-irreducible element n_i."
   [layout n_i part information]
   (let [upper-neighbours (:upper-neighbours-of-inf-irrs information),
-	inf-irrs (:inf-irrs information),
+	phi_0 (:phi_0 information),
 	positions (first layout),
 
 	pos-n_i (positions n_i),

						 [(+ x top-x), (+ y top-y)])
					       (vals placement))))]

    ;; (pprint placement)
    [placement connections]))



    (* 2 (sum [[v_1 v_2] edges,
	       :when (and (order [v_1 n_i])
			  (not (order [v_2 n_i])))]
	    (- (nth (pos v_2) part) (nth (pos v_1) part))))))


;; Gravitative Energy and Force
